Ask Tom why: Chicago's blizzard in early February makes me curious as to the differences, if any, between a blizzard and a snowstorm.

March 26, 2011

Dear Tom,

Chicago's blizzard in early February makes me curious as to the differences, if any, between a blizzard and a snowstorm.

—Stan Mudrak

Dear Stan,

Meteorological jargon often finds its way into general use, but the precise definitions of those terms sometimes get lost. Meteorologically, the distinction between a snowstorm and a blizzard is significant.

A snowstorm is a generic term for any storm with lots of new snow, whereas a blizzard, a special and very rare event in Chicago, is a severe winter storm with sustained winds of 35 mph or higher and sufficient falling and/or blowing snow to reduce visibility to less than 0.25 mile for at least three hours. Note that falling snow, in and of itself, is not a necessary condition.